Differential effects of temperature blockade on the proteolytic processing of three secretory granule-associated proteins

1994 ◽  
Vol 107 (3) ◽  
pp. 737-745 ◽  
Author(s):  
S.L. Milgram ◽  
R.E. Mains
Keyword(s):  
Endoplasmic Reticulum ◽  
Secretory Pathway ◽  
Proteolytic Processing ◽  
Prohormone Convertase ◽  
Trans Golgi Network ◽  
Processing Enzymes ◽  
Prohormone Convertase 1 ◽  
Associated Proteins ◽  
Mouse Pituitary ◽  
Golgi Network

Vesicular transport within the secretory pathway can be arrested by incubating cells at 15 degrees C or 20 degrees C to block exit from the endoplasmic reticulum or trans-Golgi network, respectively. Using this powerful tool we have compared the intracellular sites of endoproteolytic processing of proopiomelanocortin and two prohormone processing enzymes in AtT-20 mouse pituitary corticotrope tumor cells. For comparison, proopiomelanocortin processing was also evaluated in primary neurointermediate pituitary cultures. AtT-20 cells synthesize and store endogenous proopiomelanocortin and prohormone convertase 1; AtT-20 cells expressing high levels of integral membrane or soluble peptidylglycine alpha-amidating monooxygenase were generated by stable transfection. Cells were incubated with [35S]methionine and chased at 4 degrees C, 15 degrees C, 20 degrees C or 37 degrees C. The endoproteolytic processing of peptidylglycine alpha-amidating mono-oxygenase, prohormone convertase 1, and proopiomelanocortin was compared following immunoprecipitation. Endoproteolytic processing of integral membrane and soluble peptidylglycine alpha-amidating monooxygenase proteins was completely blocked by incubation of cells at 20 degrees C. In contrast, prohormone convertase 1 processing from the 87 kDa precursor to the 81 kDa intermediate proceeded to completion at both 15 degrees C and 20 degrees C, while cleavage to generate the 63 kDa prohormone convertase 1 protein was completely blocked at 20 degrees C. In AtT-20 cells and neurointermediate pituitary cultures, generation of beta-lipotropin from proopiomelanocortin continued at a slow but significant rate at 20 degrees C, while processing of beta-lipotropin to beta-endorphin was blocked. Thus prohormone convertase 1 processing begins in the endoplasmic reticulum and is not completed until after the trans-Golgi network, while peptidylglycine alpha-amidating monooxygenase processing begins after the trans-Golgi network. Selected proopiomelanocortin cleavages begin before entry into immature granules.

scholarly journals Ionic milieu controls the compartment-specific activation of pro-opiomelanocortin processing in AtT-20 cells.

1995 ◽  
Vol 6 (10) ◽  
pp. 1271-1285 ◽  
Author(s):  
W K Schmidt ◽  
H P Moore
Keyword(s):  
Intracellular Transport ◽  
Secretory Pathway ◽  
Intact Cell ◽  
Secretory Granules ◽  
Cell System ◽  
Proteolytic Processing ◽  
Prolonged Incubation ◽  
Trans Golgi Network ◽  
Processing Enzymes ◽  
Golgi Network

Newly synthesized prohormones and their processing enzymes transit through the same compartments before being packaged into regulated secretory granules. Despite this coordinated intracellular transport, prohormone processing does not occur until late in the secretory pathway. In the mouse pituitary AtT-20 cell line, conversion of pro-opiomelanocortin (POMC) to mature adrenocorticotropic hormone involves the prohormone convertase PC1. The mechanism by which this proteolytic processing is restricted to late secretory compartments is unknown; PC1 activity could be regulated by compartment-specific activators/inhibitors, or through changes in the ionic milieu that influence its activity. By arresting transport in a semi-intact cell system, we have addressed whether metabolically labeled POMC trapped in early secretory compartments can be induced to undergo conversion if the ionic milieu in these compartments is experimentally manipulated. Prolonged incubation of labeled POMC trapped in the endoplasmic reticulum or Golgi/trans-Golgi network did not result in processing, thereby supporting the theory that processing is normally a post-Golgi/trans-Golgi network event. However, acidification of these compartments allowed effective processing of POMC to the intermediate and mature forms. The observed processing increased sharply at a pH below 6.0 and required millimolar calcium, regardless of the compartment in which labeled POMC resided. These conditions also resulted in the coordinate conversion of PC1 from the 84/87 kDa into the 74-kDa and 66-kDa forms. We propose that POMC processing is predominantly restricted to acidifying secretory granules, and that a change in pH within these granules is both necessary and sufficient to activate POMC processing.

Immunoisolation of Kex2p-containing organelles from yeast demonstrates colocalisation of three processing proteinases to a single Golgi compartment

1993 ◽  
Vol 106 (3) ◽  
pp. 815-822
Author(s):  
N.J. Bryant ◽  
A. Boyd
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Secretory Pathway ◽  
High Yield ◽  
Trans Golgi Network ◽  
Processing Enzymes ◽  
Terminal Domain ◽  
Golgi Compartment ◽  
Functional Equivalent ◽  
Golgi Network

One of the Golgi compartments of Saccharomyces cerevisiae is defined by the presence of a specific endoproteinase, Kex2p, which cleaves precursor polypeptides at pairs of basic residues. We have used antibodies directed against the cytoplasmically disposed C-terminal domain of Kex2p to develop an immuno-affinity procedure for the isolation of Kex2p-containing organelles. The method gives a high yield of sealed organelles that are essentially free of contamination from other secretory pathway organelles while being significantly enriched for two other late Golgi enzymes, dipeptidylaminopeptidase A and the Kex1 carboxypeptidase. Our findings provide clear evidence for a single yeast Golgi compartment containing all three late-processing enzymes, which is likely to be the functional equivalent in yeast of the mammalian trans-Golgi network.

Molecular chaperones in pancreatic tissue: the presence of cpn10, cpn60 and hsp70 in distinct compartments along the secretory pathway of the acinar cells

1994 ◽  
Vol 107 (3) ◽  
pp. 539-549 ◽  
Author(s):  
C.S. Velez-Granell ◽  
A.E. Arias ◽  
J.A. Torres-Ruiz ◽  
M. Bendayan
Keyword(s):  
Endoplasmic Reticulum ◽  
Golgi Apparatus ◽  
Secretory Pathway ◽  
Secretory Granules ◽  
Acinar Cells ◽  
Pancreatic Tissue ◽  
Secretory Proteins ◽  
Trans Golgi Network ◽  
Hsp70 Protein ◽  
Golgi Network

Three chaperones, the chaperonins cpn10 and cpn60, and the hsp70 protein, were revealed by immunochemistry and cytochemistry in pancreatic rat acinar cells. Western immunoblotting analysis of rat pancreas homogenates has shown that antibodies against cpn10, cpn60 and hsp70 protein recognize single protein bands of 25 kDa, 60 kDa and 70 kDa, respectively. Single bands for the cpn10 and cpn60 were also detected in pancreatic juice. Immunofluorescence studies on rat pancreatic tissue revealed a strong positive signal in the apical region of the acinar cells for cpn10 and cpn60, while an immunoreaction was detected at the juxtanuclear Golgi region with the anti-hsp70 antibody. Immunocytochemical gold labeling confirmed the presence of these three chaperones in distinct cell compartments of pancreatic acinar cells. Chaperonin 10 and cpn60 were located in the endoplasmic reticulum, Golgi apparatus, condensing vacuoles and secretory granules. Interestingly, the labeling for both cpn10 and cpn60 followed the increasing concentration gradient of secretory proteins along the RER-Golgi-granule secretory pathway. On the contrary, the labeling for hsp70 was mainly concentrated in the endoplasmic reticulum and the Golgi apparatus. In the latter, the hsp70 was found to be primary located in the trans-most cisternae and to colocalize with acid phosphatase in the trans-Golgi network. The three chaperones were also present in mitochondria. In view of the role played by the chaperones in the proper folding, sorting and aggregation of proteins, we postulate that hsp70 assists the adequate sorting and packaging of proteins from the ER to the trans-Golgi network while cpn10 and cpn60 play key roles in the proper packaging and aggregation of secretory proteins as well as, most probably, in the prevention of early enzyme activation in secretory granules.

scholarly journals Prohormone convertase 1 (PC1) processing and sorting: effect of PC1 propeptide and proSAAS

2004 ◽  
Vol 182 (2) ◽  
pp. 353-364 ◽  
Author(s):  
SN Lee ◽  
E Prodhomme ◽  
I Lindberg
Keyword(s):  
Secretory Pathway ◽  
Serine Proteinase ◽  
Significant Inhibition ◽  
Proteolytic Processing ◽  
Hek293 Cells ◽  
Prohormone Convertase ◽  
Prohormone Convertase 1 ◽  
In Trans ◽  
Regulated Secretory Pathway ◽  
Carboxy Terminal

Prohormone convertase 1 (PC1) is a serine proteinase responsible for the proteolytic processing of many precursor proteins within the regulated secretory pathway. The activity of PC1 is potentially regulated by two endogenous inhibitors, the PC1 propeptide and proSAAS. Here we have investigated the effect of proSAAS and propeptide-containing constructs on PC1 carboxy-terminal processing and activity. In AtT-20 cells, proSAAS expression inhibited both C-terminal PC1 processing and proopiomelanocortin (POMC) processing under pulse/chase conditions. SAAS CT peptide-propeptide chimeric constructs had no effect on the cleavage of PC1 and POMC under pulse/chase conditions. However, a construct containing the propeptide alone reduced C-terminal PC1 processing under pulse/chase conditions and also inhibited POMC processing. In contrast, experiments using HEK293 cells transiently expressing PC1 plus the respective constructs demonstrated significant inhibition of zymogen processing and decreased C-terminal processing of PC1 by the SAAS CT peptide portion of the chimera. Our results suggest that the PC1 propeptide expressed in trans is able to act as an endogenous inhibitor of PC1, but that SAAS CT peptide-containing/propeptide constructs cannot function as effective inhibitors of precursor maturation in the regulated pathway.

scholarly journals Detection of angiotensin II‐induced Ras activation in the trans‐Golgi network and the endoplasmic reticulum using BRET‐based biosensors

2011 ◽  
Vol 25 (S1) ◽  
Author(s):  
Laszló Hunyady ◽  
Eszter Soltész‐Katona ◽  
László Erdélyi ◽  
Péter Várnai ◽  
András Balla
Keyword(s):  
Endoplasmic Reticulum ◽  
Angiotensin Ii ◽  
Trans Golgi Network ◽  
Ras Activation ◽  
Golgi Network

scholarly journals Adaptor protein 2–mediated endocytosis of the β-secretase BACE1 is dispensable for amyloid precursor protein processing

2012 ◽  
Vol 23 (12) ◽  
pp. 2339-2351 ◽  
Author(s):  
Yogikala Prabhu ◽  
Patricia V. Burgos ◽  
Christina Schindler ◽  
Ginny G. Farías ◽  
Javier G. Magadán ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Amyloid Precursor Protein ◽  
Secretory Pathway ◽  
Brefeldin A ◽  
Adaptor Protein ◽  
Proteolytic Processing ◽  
Precursor Protein ◽  
Amyloid Precursor Protein Processing ◽  
Intermediate Compartment ◽  
Golgi Network

The β-site amyloid precursor protein (APP)–cleaving enzyme 1 (BACE1) is a transmembrane aspartyl protease that catalyzes the proteolytic processing of APP and other plasma membrane protein precursors. BACE1 cycles between the trans-Golgi network (TGN), the plasma membrane, and endosomes by virtue of signals contained within its cytosolic C-terminal domain. One of these signals is the DXXLL-motif sequence DISLL, which controls transport between the TGN and endosomes via interaction with GGA proteins. Here we show that the DISLL sequence is embedded within a longer [DE]XXXL[LI]-motif sequence, DDISLL, which mediates internalization from the plasma membrane by interaction with the clathrin-associated, heterotetrameric adaptor protein 2 (AP-2) complex. Mutation of this signal or knockdown of either AP-2 or clathrin decreases endosomal localization and increases plasma membrane localization of BACE1. Remarkably, internalization-defective BACE1 is able to cleave an APP mutant that itself cannot be delivered to endosomes. The drug brefeldin A reversibly prevents BACE1-catalyzed APP cleavage, ruling out that this reaction occurs in the endoplasmic reticulum (ER) or ER–Golgi intermediate compartment. Taken together, these observations support the notion that BACE1 is capable of cleaving APP in late compartments of the secretory pathway.

scholarly journals A new role for RINT-1 in SNARE complex assembly at the trans-Golgi network in coordination with the COG complex

2013 ◽  
Vol 24 (18) ◽  
pp. 2907-2917 ◽  
Author(s):  
Kohei Arasaki ◽  
Daichi Takagi ◽  
Akiko Furuno ◽  
Miwa Sohda ◽  
Yoshio Misumi ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Trafficking ◽  
Retrograde Transport ◽  
Snare Complex ◽  
Initial Contact ◽  
Complex Assembly ◽  
Trans Golgi Network ◽  
Cog Complex ◽  
Protein Receptor ◽  
Golgi Network

Docking and fusion of transport vesicles/carriers with the target membrane involve a tethering factor–mediated initial contact followed by soluble N-ethylmaleimide–sensitive factor attachment protein receptor (SNARE)–catalyzed membrane fusion. The multisubunit tethering CATCHR family complexes (Dsl1, COG, exocyst, and GARP complexes) share very low sequence homology among subunits despite likely evolving from a common ancestor and participate in fundamentally different membrane trafficking pathways. Yeast Tip20, as a subunit of the Dsl1 complex, has been implicated in retrograde transport from the Golgi apparatus to the endoplasmic reticulum. Our previous study showed that RINT-1, the mammalian counterpart of yeast Tip20, mediates the association of ZW10 (mammalian Dsl1) with endoplasmic reticulum–localized SNARE proteins. In the present study, we show that RINT-1 is also required for endosome-to–trans-Golgi network trafficking. RINT-1 uncomplexed with ZW10 interacts with the COG complex, another member of the CATCHR family complex, and regulates SNARE complex assembly at the trans-Golgi network. This additional role for RINT-1 may in part reflect adaptation to the demand for more diverse transport routes from endosomes to the trans-Golgi network in mammals compared with those in a unicellular organism, yeast. The present findings highlight a new role of RINT-1 in coordination with the COG complex.

scholarly journals Proteomic Characterization of Isolated Arabidopsis Clathrin-Coated Vesicles Reveals Evolutionarily Conserved and Plant Specific Components

2021 ◽  
Author(s):  
Dana A. Dahhan ◽  
Gregory D. Reynolds ◽  
Jessica J. Cárdenas ◽  
Dominique Eeckhout ◽  
Alexander Johnson ◽  
...  
Keyword(s):  
Secretory Pathway ◽  
Adaptor Protein ◽  
Coated Vesicles ◽  
Mass Spectrometry Analysis ◽  
Chemical Labeling ◽  
Spectrometry Analysis ◽  
Trans Golgi Network ◽  
Evolutionarily Conserved ◽  
Golgi Network

In eukaryotes, clathrin-coated vesicles (CCVs) facilitate the internalization of material from the cell surface as well as the movement of cargo in post-Golgi trafficking pathways. This diversity of functions is partially provided by multiple monomeric and multimeric clathrin adaptor complexes that provide compartment and cargo selectivity. The adaptor-protein AP-1 complex operates as part of the secretory pathway at the trans-Golgi network, while the AP-2 complex and the TPLATE complex (TPC) jointly operate at the plasma membrane to execute clathrin-mediated endocytosis. Key to our further understanding of clathrin-mediated trafficking in plants will be the comprehensive identification and characterization of the network of evolutionarily conserved and plant-specific core and accessory machinery involved in the formation and targeting of CCVs. To facilitate these studies, we have analyzed the proteome of enriched trans-Golgi network/early endosome-derived and endocytic CCVs isolated from dividing and expanding suspension-cultured Arabidopsis cells. Tandem mass spectrometry analysis results were validated by differential chemical labeling experiments to identify proteins co-enriching with CCVs. Proteins enriched in CCVs included previously characterized CCV components and cargos such as the vacuolar sorting receptors in addition to conserved and plant-specific components whose function in clathrin-mediated trafficking has not been previously defined. Notably, in addition to AP-1 and AP-2, all subunits of the AP-4 complex, but not AP-3 or AP-5, were found to be in high abundance in the CCV proteome. The association of AP-4 with suspension-cultured Arabidopsis CCVs is further supported via additional biochemical data.

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